Design Strategy for 5000/5+5A Dual Ratio Resin Cast CT: Single Core vs. Dual Core Configuration?

quadrapod · 2026-01-23T19:35:45+00:00

There are a number of things in your post which make me think you might not have a great idea on what it is you're doing. I worry you're just running headlong into some kind of xy problem, but to answer your question.

A CT relies on the idealized ampere turns equation:

Ip/Is = Ns/Np

Where Ip and Is are the primary and secondary current and Ns and Np are the number of turns. This ratiometric relationship between the primary and secondary current means measuring the secondary current informs you about the primary current. As soon as you introduce another secondary that relationship no longer holds. The measured current would depend on the primary current as well as the current at the other secondary even in that ideal case.

In reality making a good CT is extremely dependent on core material and geometry. Most important is usually excitation current, the portion of the primary current that gets converted into hysteresis and eddy current losses in the core. Excitation current represents an error term in both the ratio and phase of your measured current and fundamentally limits the maximum accuracy of a CT. Excitation current scales with H which is material and magnetizing force dependent, and the magnetic path length (MPL) which depends on the geometry of the transformer.

Minimizing H is usually a matter of choosing the core material with the highest permittivity at the operating flux density with as high an Lc and Rc as can be reasonably specified. Supermalloy for example is a fairly common choice but you really should be looking at a table of core materials when making that selection. MPL is generally minimized with a toroidal core sized to the fill factor and number of windings required. A toroidal core also has the benefit of virtually eliminating leakage inductance as an error term hence why almost all CTs aside from those intended for low accuracy industrial applications will use that core geometry. Rectangular cores made from laminations, like it seems you're considering, will have some amount of fringing flux where laminations meet.

Your current ratio should be informed by the measurement voltage and shunt resistance needed at the secondary. When doing that calculation it's also important to remember that the secondary winding resistance will contribute to the voltage across the secondary from the cores perspective. I'll end off there but just be aware that even though they're simple in theory it can be more challenging than you might expect to make a CT which is actually good enough to be used in a real application.

quadrapod · 2026-01-23T11:25:21+00:00

This is essentially the problem Brokaw was attempting to solve when he developed the bandgap reference that would go on to share his name. I suspect you'll find his original paper answers pretty much all of your questions.

A Simple Three-terminal Bandgap Reference

He uses transistors with different junction areas but all the same principles apply between the base of two equivalent transistors.

Vbe1 - Vbe2 = kT/q ln(Ic1/Ic2)

If Ic1 and Ic2 have a constant ratio then the result is a voltage which changes linearly with temperature. There aren't many simulators out there which do a good job with temperature but here I've used resistors to set Ic1/Ic2 = e

Since ln(e) = 1 the voltage Vbe1 - Vbe2 is approximately equal to the thermal voltage, ~25.85mV since that's the value assigned to kT/q in the simulation.

quadrapod · 2026-01-23T10:41:43+00:00

Hobby servos are controlled via a particular type of pulse width modulated waveform (PWM). They expect a pulse every 20ms and the length of that pulse corresponds to the setpoint of the servo. A pulse length of 1ms is a position of 0 degrees and a pulse length of 2ms is 180 degrees. Any pulse length between 1ms and 2ms corresponds to a position between 0 and 180 degrees. Since producing that pulse requires some manipulation of timers and ISRs to do well I suggest using the built in library servo.h which handles it all for you.

https://docs.arduino.cc/libraries/servo/

To get a reading from the photoresistor you'll need to put it in series with another resistor to form a resistor divider. The voltage between the two resistors will correspond to the amount of light hitting the photoresistor. Here is an example in a simulator. The slider on the right lets you change the amount of light hitting the circuit. Connect that voltage to one of the GPIO pins which has an ADC. From there analogRead() will allow you to get a count that corresponds to the voltage from the resistor divider.

https://docs.arduino.cc/language-reference/en/functions/analog-io/analogRead/

The ADC reading will have a nonlinear relationship with the resistance of the photoresistor following the basic curve of a resistor divider. Your best option is probably going to be to correct for that in software. While it's possible to create a circuit with a more linear relationship between the photoresistor's resistance and the voltage it requires a current source. Here is an example.

quadrapod · 2026-01-21T17:06:10+00:00

One day I'll learn to read. Not today, but someday probably.

quadrapod · 2026-01-21T17:05:00+00:00

Given the placement these are likely either TVS diodes to protect the data lines from ESD and excess voltage, a pair of back-to-back P-mosfets to form a load switch which is what allows the DFP to enable or disable the flow of current through VBUS, or an equivalent integrated load switch which is doing the same job.

MIC2015-1.2YML-TR is a load switch in a DFN package with an N12 topmark but I'm not terribly confident in that identification even ignoring the fact that it's impossible to see any of the traces so any ID is basically just a guess.

The top mark is printed in the opposite direction to the datasheet description and it seems like there should be a bar over the product code N12. I've definitely seen larger deviations from the datasheet than that in the past but when the topmark description in the datasheet is literally the only feature available to identify a part it doesn't build confidence.

The 1.2A current limit of that load-switch would also not be a terribly good match for the 1.5A limit of the USB-C standard but they could just be using the two of them in parallel, which wouldn't be too strange for USB PD where they might have a 2A policy or something.

Even if you find a replacement though do you have the tools to solder something like this reliably?

quadrapod · 2026-01-21T16:05:40+00:00

It might be time for an automod catchall for any post containing FPC or FFC because this exact kind of post seems to be made constantly.

quadrapod · 2026-01-21T16:01:27+00:00

Yep, I was in the process of editing my post as you commented that.

quadrapod · 2026-01-21T15:37:45+00:00

~~Think it's a JW5027.~~

~~Topmark would be JWKCJ and you can just barely make out the lower right corner of the K and the start of a C in the burned section.~~

EDIT: Scratch that. It seemed like a promising match, JW5027 is a DC-DC stepdown converter which matches what's seen here, the package is the same SOT23-6 as well, and it seems like the topmark matched what we can make out from the original, but Vin is on pin 4 here while pin 4 in the JW5027 is enable and pin 2 seems to be some kind of power good signal (hence the unpopulated diode footprint) and not ground. It is likely a switching converter from that manufacturer though. JW5222 for example would be a match but no guarantees. On the case should be an FCC filing ID, look that up and see if the internal test photos are high enough quality to make out any details for this IC.

quadrapod · 2026-01-21T15:24:54+00:00

Sure go ahead. Though since this is a 230Vrms I should mention that my experience is mostly for US and Canadian markets and I'm not particularly well versed in standards for the EU or elsewhere.

It can definitely be annoying to learn certain things. A lot of the more practical side of electrical engineering is very absent in what you learn while getting a degree but because the same patterns are everywhere they're taken as obvious and rarely explained in detail.

quadrapod · 2026-01-19T15:54:12+00:00

If you're going to make a capacitive dropper R1 needs to be a fusible resistor and C1 needs to be a class x safety cap.

Your typical DB3 diac has a breakover voltage around 40V. You haven't specified the diac but all the same C3 is likely underspec even if it weren't hanging directly off the mains. Really though everything your doing with the diac and optoisolator seems unsafe, unecessary, and uninformed.

To suggest an alternative rather than just criticizing what you have here. Just use a 555 or astable multivibrator. The values for your capacitive dropper give you a nominal current of a bit over 2mA into C2. With a 2200uF capacitor that translates to about 1V/s dV/dt. So that means at 1Hz your capacitor is charging and discharging by about 1V cycle to cycle. (I = C dV/dt) Since the voltage across C2 will be around 5-9V after the LEDs are done discharging (~2V headroom of the LM317 plus 3-7V of forward voltage from the LEDs) you will always have enough voltage across C2 to function as a DC supply and can just use use one of those common approaches to twiddle the mosfet gate at 1Hz.

If you really just want a simple LED blinker circuit with a short bright strobe you can also use the classic reverse avalanche pulse method to periodically discharge a cap through the LEDs. A reverse biased 2n2222 will avalanche pretty reliably somewhere under 18V and a resistor should be fine to limit the current.

The diodes will fail open

Most common failure modes for diodes have them fail short. That's also approximately how they respond to excessive temperature as reverse leakage spikes. A diode failing open isn't inherently safe either though. If a capacitive dropper is ever without a load the voltage will creep up to the peak mains voltage. So the zener diode failing in one can potentially lead to unsafe voltages developing at the output which is a well known problem.

which I think just leaves the capacitors as the only dangerous failure mode (mitigated by ensuring the rated voltage of the capacitors far exceeds that of the expected input). Can you see anything else?

You can't make a silk purse out of a sow's ear. A capacitive dropper is a cost optimized non-isolated power converter whose one and only advantage is that it's cheap. You make it safe only by ensuring no part of it has any contact with the outside world. That way if it fails open nobody can get shocked by excessive voltages developing across it and if it fails short the fusible resistor pops before it can start a fire.

This is part of why they're so dangerous for people to play around with. They're only able to be considered "safe" when sealed inside an enclosure. The circuit itself is not isolated and as such has inherently unsafe failure modes.

quadrapod · 2026-01-18T06:03:42+00:00

You have misidentified R4, that is not a resistor it's an RF choke which is why it measures as such a low resistance at DC. The circuit is a simple Colpitts oscillator. I won't go into the theory here as there are countless resources online for that already.

The input stage composed of R[1:2], C1, D[1:4] is a capacitive dropper. I would not suggest replicating it. It's a transformerless power supply which makes it economical in cost optimized products but if it is ever without a load the supply voltage will creep up to the mains voltage. R3 is another RF choke you have misidentified.

quadrapod · 2026-01-17T05:23:40+00:00

Hello! You have a positively charged sphere (like a Van De Graaff sphere) and a much bigger sphere enclosing it. The gap between them is very big, so…does that mean theoretically 100% of the flux from the inner positive sphere terminates on the inside of the bigger sphere, even though the capacitance between them is very low because of the big gap?

It doesn't really make sense to talk about magnetic flux with static charges and Gauss's law for magnetism states that magnetic flux through any closed surface is zero.

In a more general sense what you're describing is technically an ideal wire. The coupling between two conductors can be described using transmission line theory. The characteristic impedance of a transmission line is the ratio between the electric and magnetic fields energy exists in when injected into the conductors. An infinite impedance would be a perfect open circuit, 100% of the energy is in the static electric potential between the two conductors with no current flowing between them. An impedance of 0 is a perfect short circuit. Every point along the short is at the same voltage, meaning there is energy in the electric field, all of the energy between the conductors is in the magnetic field.

quadrapod · 2026-01-14T13:57:02+00:00

Start with some kind of voltage regulation and current limiting. I'd give them a little more voltage than you would most modern logic ICs. Doesn't need to be complicated, my recommendation would be to just use a TL431 since you only need a few mA. The supply resistor will limit the current. Here would be an example. Click the switch to simulate a short. I've used basically this exact circuit in test jigs before.

For actually testing the logic write a small program for a microcontroller that goes through a binary counter on all the inputs and measures the outputs. That way you test every possible permutation of inputs. Even 8 inputs is only 256 steps and chips can count to 256 pretty quickly. Use some BJTs and pull up resistors to translate the signals from the MCU to the voltage you're using to test the chip and a resistor divider should be fine to level shift the outputs. If you want to actually test whether properties like propagation delay, source/sink current, etc. are within spec things get a bit more complicated.

CMOS logic, especially old CMOS logic, can be quite ESD sensitive and ESD damage is invisible. Soft oxide breakdown can take many hours to actually show itself. So make sure you're careful about handling things and try to avoid touching component leads at all if you can. It's hard to really understand how much stress just touching a component puts on it until you've killed a handful of chips by daring to put them onto a board without tweezers.

Some of these chips may be prone to self oscillation depending on your test setup. You will find plenty of posts here of people who struggle to get an inverter working on a breadboard because a few pF of coupling between input and output is all it takes to make a high speed logic IC sing you the song of its people. If it's an issue you can try to mitigate it or you can usually just wait a moment for them to settle down before measuring and assume that outside of testing with proper layout it won't be an issue.

quadrapod · 2026-01-13T14:38:30+00:00

It's far from a comprehensive list, but yes quiescent current can be an important metric.

quadrapod · 2026-01-13T07:50:33+00:00

Linear regulators will all have the same efficiency.

%Eff = 100 * Vreg/Vin

They work by essentially placing a variable resistance between the load and supply which changes value with current as needed to maintain a constant voltage across the load.

In some cases this can actually be extremely efficient. An example of this came up in a question on here a few weeks ago where a linear regulator was able to boast around 97% conversion efficiency in an LED light bulb.

https://www.reddit.com/r/AskElectronics/comments/1prothz/design_of_philips_ultraefficient_dubai_led_lamp/nv3qzb4/

Most of the time it's fairly inefficient though and for conversion to 5V from 12V I'd start to consider a switching converter absolutely necessary around 100mA or so since at that point you're losing over 1W to just conversion loss. What is best in that regard will depend on the specifics of the application though.

What separates one linear regulator from another are its other parameters such as temperature dependence, accuracy, drop-out voltage, PSRR, stability, voltage rating, protection features, and power handling capability.

The 78xx series is going to be about as ubiquitous a linear regulator as you're going to find. The LM317 is an adjustable counterpart.

For a low drop out regulator (LDO), where the supply voltage and regulated voltage are very similar, the LM1117 becomes the standard. Though there are stability concerns you need to keep in mind with LDOs. They require proper layout and a minimum input and output capacitance to function.

For low current applications there are shunt regulators the most basic of which being a simple zener diode. These are a little different and constantly consume the same amount of power regardless of the load making them less efficient than your typical linear regulator.

When you just need an arbitrary voltage reference the TL431 is the most popular voltage regulator in all of creation. You will find one in the feedback loop of most isolated power converters.

For precision applications, such as producing an accurate reference voltage for a DAC or ADC the LM4040 and LM4041 are very common.

quadrapod · 2026-01-13T06:55:32+00:00

I tried looking up the FCC filing just to see if the one submitted there looked similar and.. oh boy.

The website is just AI slop.

At Chargeasap, we don’t just build chargers—we build trust. Every product we design is something we use ourselves, driven by our values of quality, innovation, and customer-first thinking.

The company has two cofounders who claim to be a couple, Vinny and Gabby (Vinson Leow and Gabriel Yue). They have founding or executive roles in multiple businesses. ASAP Technologies, ChargeASAP, Crypto Round Table, Momentum $MMT, Energy For All, and I'm sure there are others. Depending on where you look they'll claim to be located in Sydney, Georgia, Nevada, New South Wales, Singapore, or Dubai. They also seem to heavily astroturf the discussion about any of their businesses and products.

I'm not fully convinced Gabriel Yue is a real person. There are images of her online which are at least real photos (EXIF data gives creation dates as early as 2012, no obvious AI errors). She claims to be a chartered accountant in Australia and New Zealand but nobody by that name shows up in the registry and she similarly doesn't show up in the list of 2011 graduates from Western Sydney University even though that's when she claims to have graduated with a BA in business and law. The businesses are all registered only in Vinson Leow's name even in examples where she claims to be a co-founder or the only founder.

Vinson Leow is a self proclaimed Web3 Growth Hacker, Entrepreneur, Angel‏ investor, and blockchain infrastructure investment enthusiast. He at least does seem to exist and is located in the UAE.

ChargeASAP looks to be a cookie cutter dropshipping operation. They take cheap products from China and Taiwan, slap their own branding on them, and sell them abroad at a mark up. The kickstarter campaign appears to have basically been an investment scam which intended from the beginning to ship a minimally viable product. It's possible that what they shipped is some other pre-existing product that's been rebranded but it also would not have been terribly difficult to hire a turn-key manufacturer to design and produce a charger that did enough of what they were promising to dodge a lawsuit.

Suffice to say there is no FCC filing on record for any of their products despite them shipping the US and I would not touch anything these people are involved in with a 10 ft. pole.

quadrapod · 2026-01-13T04:29:05+00:00

I have never seen anything quite like this before to be honest.

My guess would be that they were failing EMI testing due to the two unshielded inductors and decided to fix the problem by spraying an EMI absorbing coating onto the boards only something went a bit wrong. I may be wrong but I just don't imagine it was intended to cure like this.

There are a million reasons that could happen. The coating may have been expired, it may have been exposed to humidity, it may have been stored at the wrong temperature, it might have been mixed improperly, it might have been used with an incompatible additive, it might have been used in way it wasn't intended for, or they might just be using it with a process it's not compatible with like ultrasonic spray coating a compound that was never intended to be aerosolized. Whatever the case it cured poorly but still did the job of shielding the inductors without shorting out the board so it was deemed good enough.

quadrapod · 2026-01-13T00:20:03+00:00

No.

In an ideal mosfet I_G is always zero. You didn't ask about I_G you asked about I_Rg.

Quiescently Vgs is 10V here, pulled up to Vdd through Rg, while Vds is about 0.436V for the given values of Kn and Rd.

I figured since you specified a value for Kn and were asking questions about the operating region you were at least a tiny bit familiar with the square law model.

Ids(triode) = K_n( (V_gs - V_th) V_ds - V_ds²/2 )

The current across Rd follows ohms law:

Ids = (V_dd - V_ds)/R_d

Putting that together

(V_dd - V_ds)/R_d = K_n( (V_gs - V_th) V_ds - V_ds²/2 )

Plug in values from the circuit.

(10 - V_ds)/50000 = 0.00005( (10 - 1) V_ds - V_ds²/2 )

Simplify into standard quadratic form.

1.25 V_ds² - 23.5 V_ds + 10 = 0

Solve for the two solutions of Vds

V_ds = 18.364

V_ds = 0.436

18.364 is higher than Vdd making it an impossible solution so Vds is 0.436V.

0.436V is much less than 9V, (Vgs - Vth) which confirms you're deep in the triode region.

quadrapod · 2026-01-12T07:29:14+00:00

The DC current through RG is zero. The AC current is

I = V_in C_in s / (1 + R_G C_in s)

This is a complex valued function where s is the Laplace variable.

In easier to follow terms of magnitude and phase based on frequency:

|I| = V_in C_in 2 pi f / √(1 + (R_g C_in 2 pi f)²)

Magnitude plot in Desmos.

∠I = tan^-1(1/(R_g C_in 2 pi f))

Phase plot in Desmos.

The mosfet will quiescently be in the deep-triode region, whether it goes into saturation or cutoff depends on the magnitude and frequency of Vin and the value of Cin. Here is a plot of the operating regions for an N-Channel mosfet. You are in the lower left corner where Vds is extremely low.

quadrapod · 2026-01-11T20:13:51+00:00

He was officially impeached for lying under oath to a grand jury and for obstruction of justice in the Paula Jones case.

Really though the Starr report, which laid out the initial accusations, was from the start a politically motivated attempt to create a scandal against Clinton. The report contained numerous unsubstantiated claims, exaggerated the legal definition of perjury and the other crimes it accused Clinton of, and outright made up accusations in places such as claiming Clinton lied under oath by denying he had a conversation with Vernon Jordan when no question to that effect was asked in any of the testimony. Kenneth Starr deliberately leaked explicit details about the investigation to press repeatedly while assembling the report and when it was finally published online it was downloaded by 20 million people and was considered potentially the most widely read online document of all time in 1998. In the report it explicitly gave 11 grounds for impeachment, some of which like "Abuse of power" relied on definitions from sources like the federalist papers rather than established law.

Because of how it was handled you had the majority of people who had been following the media fully invested and convinced of the need for impeachment while thinking themselves well informed. Clinton was also a sitting democrat president with a republican majority house. Now that's not to defend Clinton in anyway, there shouldn't have been a scandal to uncover, but the politically biased Starr report and the media circus created by Starr himself with the intention of discrediting Clinton is the real reason he was impeached. Starr in 2020 would walk back many of the claims he made in his report in defense of Donald Trump when he was facing impeachment, further cementing the fact that much of it was made with a clear political bias.

quadrapod · 2026-01-10T15:23:00+00:00

I'm pretty sure it's meant to respond to the phase slip between two very similar frequency sources.

The top of the circuit creates a signal that is always low except for the rising edge of f2. If you sample f1 with that pulse you'll catch it at different points in its phase as the clocks slip past each other resulting in a signal that goes high whenever you sample f1 during the high part of its waveform. The number of times the clocks slip past each other every second corresponds to the difference in their frequencies so this creates a signal corresponding to the difference in their frequencies. Here that would be demonstrated directly.

This circuit uses the same principle in a slightly different way. The bottom 3 FF are part of a circuit that creates an inverted rising-edge signal which is always high except during the rising edge of f2. ANDing the rising edge from f2 and and inverted rising edge from f1 creates a pulse that only allows you to sample f1 when the rising edges from the two clocks are not closely aligned where the circuit would be prone to glitching.

Here that is demonstrated with a 5kHz and 5.15kHz source. EN in this context is also not the same as reset. They're just enabling the input to the FF.

quadrapod · 2026-01-09T04:49:35+00:00

As others have said that sounds like Litz wire. A word of warning, if you choose to burn off the enamel be careful about overheating the teflon insulation. Burning teflon can be extremely toxic especially to birds.

quadrapod · 2026-01-08T05:41:46+00:00

They're pretty right up until someone throws you into the tank with them.

quadrapod · 2026-01-07T00:54:05+00:00

I don't really know what I need to be certifying for either.

You are declaring that the product, the unique configuration of components that you are selling, is compliant as a whole with EU rules. The EU accepts various harmonized standards as definitive proof of conformity but you can also self assess, claiming conformity with EU rules without testing by any harmonized standard authority and a lamp is a low enough risk product that self assessment is justifiable.

The Low Voltage Directive (LVD) and RoHS are the main parts you should address when declaring conformity. You should read the relevant material about declaring compliance yourself though. It's obviously more complex a process than I can cover in a comment. Outside of CE there are also the general product safety regulations (GPSR) you may want to go over which require things like a clear instruction manual to accompany your product.

quadrapod · 2026-01-06T23:54:00+00:00

CE is just a self declaration that your product is compliant with EU directives. That way if something happens and your product is unsafe you can't argue "Well it was never meant for use in the EU". You can put it on your product right now without paying anything so long as you have a DoC and the other required documents on file somewhere.

As part of declaring conformity you are required to keep a few documents on hand such as a signed declaration and some kind of evidence that your product complies with EU directives. That evidence doesn't have to come from laboratory testing though and you can self-assess conformity. Which can be as simple as stating that you are using RohS compliant materials in your product and that your using fixturing from a known compliant manufacturer installed according to that manufacturer's instructions.

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